This proposal has the aim of contributing to our understanding of how cells control the expression of their different collagen genes. Such a study on collagen genes is particularly important because of the extraordinary ubiquity and importance of collagen in vertebrate organisms. Each vertebrate cell carries the genes for at least 5 distinct collagen chains, yet expresses only a particular subset of these at any one developmental stage. Some promising cell-culture systems for the control of these genes available. The first objective is to isolate pure samples of collagen mRNAs from chick embryos. Not only will the structure of these mRNAs be studied, but these mRNAs will also be used as templated to make complementary DNAs (cDNAs) which will be cloned. These cDNAs will be used as tools to study the turnover of collagen mRNAs in cultured cells which are undergoing a change in collagen gene expression. They will also be used to study the organization of collagen genes and as assays for the purification of these genes. Fragments of these genes that are likely to be involved in the control of gene expression will be cloned and their structure determined.